test: explanatory comments [c-g]*

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5656103
diff --git a/test/gc1.go b/test/gc1.go
index 190b29b..6049ea1 100644
--- a/test/gc1.go
+++ b/test/gc1.go
@@ -4,6 +4,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// A simple test of the garbage collector.
+
 package main
 
 func main() {